Process for the production of chromite blocks



scientific sense the term Patented 'Apr. 13, 1943 PROCESS FOR, THEPRODUCTION OF CHROMITE BLOCKS Konrad Erdmann, Radenthein, Austria;vested in the Alien Property Custodian No Drawingm Application DecemberSerialNo. 118,018. In Austria December 31, 1932 11 Claims.

My invention relates to chrome refractory brick, more particularly torefractories composed of chromite anda highlymagnesian refractoryvehicle and towniethods of making the same.

This application isa continuation in part of my application SerialrNo.683,559, filed on Aug. 3, 1933, for Refractory brick.

Whenever I use the =term.chromite" hereinafter I mean, chrome iron ore(chrome ore), a

mineral ofthe spinel groupcontaining as the 2 main constituent, besidessome gangue, a double I, oxide of iron and chromium, the chemical formu-*la oi which is FeO.Cr:Oa, partof the chromium oxide being alwaysreplaced by ferric oxide and alumina, and the iron oxide being alwayspartial- 1y replaced by magnesium oxide. Though in the fchromite meansthe pure compound FeQCrzOa, in technical language the terms chromite and"chrome iron ore are used as synonyms to denote the native mineral ofthe spinel group asspecified above.

The main object of myinvention is to provide bricks having unprecedentedresistance to sudden changes oftemperature, great slag resistance andstrength at high temperatures, and fair strength at atmospherictemperatures.

Bricks made exclusively of chromite, although otherwiseadmirably suitedfor employment as refractory material, share with those of magnesite,the unwelcome property of poor spalling-resistance. The presentinvention succeeds in' surprisingly improving chromite bricks, asregards resistance to spelling, by the combined measures in the'j'noduction of the brick of blending thetchrom'ite with a particularaddition of a m nesian'refractory and by the use of aparticularselection of grain sizes both as herein disclosed. TThis" valuableresult'is achieved according to my invention while securing bricks whichshow simultaneously great slag resistance and strength at hightemperatures and fair strength at atmospheric temperature.

a Selection of grain sizes is a measure generally known in the ceramicindustry, and one of special application in connection with'theproduction of v chromite bricks also, this having heretcforecbeen done,inrthis particular art, for the purpose of increasing as far, aspossible the density of l the 1 bricks. Proposals of this kind aredevoid qfimportance for the production of bricks capable of highlymagnesian refractory that the proportion of wlthstandingsudden changesof temperature; it has transpired that there is no necessary relationbetween density and spalling-resistance.

This resistance to spalling can be tested'by heating the brick in mg bya blast of cold compressed air at one atm.

for five minutes. The numerical values (as herematter given inconnection with the tests of spalling resistance) indicate the number ofrepetitions of heating and chilling cycles endured by 'the brick withoutany part oi the heated portion splitting away. Tested the result aimedat, in a mixture of chromite and material, containing. chromite inlarger quantity than the magnesian refractory material, the proportionof grains below 100a (passing through a 150 mesh per linear inch screen)and above 1000 (retained on a 16 mesh per linear inch screen) must beincreased relatively to the intermediate fraction.

r The foregoing and all the following data regarding sieve designationsrefer to the Tyler Standard Screen Scale (cf. nternational CriticalTables 1927, Vol. II. 330).

As a rule, in the ground material, chromite as well as magnesite, as itcomes from any kind of usual grinding devices, the amounts to'about 12to 25%, that between 100 and 1000,11. to about 40 to and that'above 1000to about 10 to 305%. According to my invention the mix is preparedinsuch a manner at least to 20 to 40%, that of the middle fraction doesnot exceed 15 to 25% and that of the coarse fraction amountsat least to35 to 65%.

In an alternative embodiment of the invention,

giving betterresults, the grains of intermediate marginal si'zesbetween'the ilneand middle frac- "tions, and/or" between the middle :andcoarse fractions respectively, are screened on and re-,

diiference of at least e smallest grain in the thesize of the largestmoved so that thereis between the size of t next coarser fraction" andan, electric furnace to 950 C. for a period 01' 50 minutes,'andtherafter chillfraction below 100a the fine fraction amounts mixture maybe at least 20% values, at all events no grain in the next finerfraction; when still better bricks are desired this difference in sizemay even be as much as from 400 up to 1000/L, correspond- (20 to 40)2(80 to 60) The proportion of magnesian refractory in the and may be ashi h'as 50% of the whole charge. A preferred mixture is one containing20 to 40%, for example about 30%, of this material It is of decisiveimportance that a preponderant part of the magnesian constituent,preferablythe whole of the same, be in a fine conditionbelow about 100p.n the other hand, it is preferable to introduce the chromite chiefly ascoarse fraction into the charge. In order to obtain the highestspallin'g particles of chromite below IOD -ought to be present in themix. The bricks are bonded with sulphite Waste liquor or with molassesor dextrine, or with other organic binders, although any suitableinorganic binder, for instance'water' glass, may also be used. I findthat about 4 to 5% of sulphite waste liquor of 20 B.-or 8%. of a 50%solution of dextrine will serve as an effective binder, the amount of-waste liquor of about 20 B., and molded under pressure of 200 to 1000kgs. per sq. cm. Finally, the molded bricks are dried, and then baked attemperatures between 1400 and l600 C.

The spalling test of the thus obtained brick is as high as 70.

ExampZeII (passing through a 32 mesh per linear inch I screen) and 1000to 1500 (between a 16 and 10 sodium silicate of 60? Be. being preferablyless than 6% or even 4%.

My invention is not intended to yield bricks of increased density. Theporosityofthebricks made according to the invention lies practicallybetween 21 and 27% while that of normal bricks on the market is'between19 and 29%. The figures given represent the apparent porosity in respectof a body, which term means the ratio of open pore space to volumeexpressed in percentages of the volume. is calculated from waterabsorption (W) and bulk density (1') .in accordance with the'formula' Ps=T.W; I V v l Example I 7 Ground chromite material containing grains 7of all sizes between 0 and 3000p. (passing through V a 7 mesh per linearinch screen) is graded into three fractions of the sizes (a) the finefraction,-

'0 to 100p (passing through a 150 mesh per linear inch screen), (1)) theintermediate-fraction, 100 to 1000 (between a 150 and 16 mesh per linearinch screen) and (c) the coarse fraction, 1000 and 3000p (between a 16and 7 mesh per linear inch screen), whereafter the grain sizes 0 to 100pare eliminated. '20 parts of the intermediate fraction 100 to 1000p and50 parts of the coarse fraction 1000 to 3000p are taken and inparts ofvery finely dicles of which are below 100 (passing through a 150 meshper linear inch screen). In order to.

The apparent porosity The material 'to be pressed is thus made up of thethree fractions specified above in such a way that the ratiobetween thefine, intermediate and-coar'se fractions is 30:20:50. These figuresrepresent mean values and can be varied in either direction to theextent of about a third. that is to say the fine magnesia fraction (0 to100,) can vary between about 20 and 40%, the

mesh per linearinch screen) are eliminated.

There remains an intermediate fraction between 500 and 1000;; anda-coarse fraction between 1500 and 3000 15 parts of the intermediatechromite fraction and 50 parts of the coarse chromite frac tion are thenintimately mixed with 35 parts of the magnesian fine meal as specifiedin'Example L, The mix is further treated in the manner described in thesaid example.

The spalling test of the thus obtained brick is as high as 70.

Example III linear inch screen) I and with 20 parts vof an extremelyfine magnesia meal prepared in the manner specified in Exampl I.

The spalling test of, the brick made in this s'w- -E:cample 1V V a 65parts of coarse chromite grain having sizes manner is as high between1000 and 19001.1. (between a 10 and 9 mesh per linear inchscreen) areintimately mixed with 35 parts of magnesia meal prepared as specified inExample I. ,This mass is worked up following the indications given inExample I.

. The bricks produced gave an average spelling test of more than 70. t

, Bricks made as described above may also be handled in an unbakedcondition, that is to say may be only dried and without previous firing,

placed in a furnace lining. Thus I use the term baking inthe followingclaims to include both kilr firing, and heating to firing temperature ina furnace lining during use'without previous kiln firing. 4 v v Allpercentages mentioned herein are percentages by weight unless thecontext clearly indicates that they are. percentages by volume, as inthe case of porosity. Referring to a certainpercentage of water solublebond, I include the water which is used as a vehicle for the bond.

Whenever I mention chromite I mean chrome ore of the type used in makingrefractory brick, that is to say a hard sort of chrome iron ore with aCrzOacontent of about 38 to 50%. Chromites of this kindare to'be takenin the raw, that is to say unburned condition. I

The term magnesia is used to include not only calcined magnesite butalso molten mag}- nesla. v

The dead-burned magnesite used may contain Il WhatIclaim is: t

I 2,316,228 j between 0.5 and 2.5% CaO. A typical analysis oi a suitabledead-burned magnesite is 1. In the process of t and strength athigh temperatures, and fair strength at atmospheric temperatures, theimprovement which comprisesadparticles in Of g ound j which the amountof said chromite is between 60 and 80%,.

Justing the proportion of the sizes of a material consisting Hessentiallychromite and ground magnesia, in

in such a manner that the mixture will contain composed of particles ofasize below 100 (passing through a 150 mesh ,perlinear inch screen),

will contain 20. to 40 stantiallycomposed of magnesia particles-of asize great strength at high temperatures and at least fair strengthatatmospheric temperatures, the

improvement which comprises adjusting the proportion of thesizes ofparticles in a material consisting essentially of ground chromite andground magnesia, in such a parts of a fine fraction subbelow about 100p:(passing through a 150 mesh Per linear inch screen) and of about 60 to80 L ipartsof a coarse fraction substantially; composed makingchromite-magnesia brick having unprecedented spallingresistance, i greatslag resistance at least about, 20 to 40 parts'of a fine fraction"notoverl5 to parts of an intermediate iracofa sizeabove about 1000a(retained on a 16 tion composed of particles of a size between about I100 and about lOOOp. (between a 150 and 16 mesh per. linear inchscreen)and at least about 35 to 65 parts of a coarse material composed ofparticles mesh per linearinch screen) substantiallyall oi the magnesiabeing-in a fine condition belowv about: 100p; (passing through a 150mesh-per linear inch screen) ,jwhereas the said fine, iracj tion belowabout 100;; contains substantially no molding the mixture ofchromite'particles of a. size above about 1000p (retained on a 1(5 meshper linearinch screen) into bricks and baking the bricks. i t

5. Refractory chromite magnesia brick composed essentially of a mixtureof particles of chromite and magnesia in which the weight of saidchromite is not less than 60%; and in which the proportion of finematerial initially smaller than 10014 (passing through a 150 mesh perlinear inch screen) is at least, about 20 to parts, the proportion ofintermediate material of initial particle sizes between 100; and 1000(between a 150 and16 mesh per linear inch screen) is not over 15 to 25parts and the proportion of coarse material of initial particle sizeabove 1000;: (retained on a 16 mesh per linear inch screen), is at leastabout 35 to 65'parts, more than one half of the magnesia being in a finestate of initial particle size below about 100 said brick beingcharacterized by'having a s'palling resistance of not below 30.

5, in which the saith i 6. Brick as defined in claim intermediatefraction is wholly omitted.

' Refractory chromite-magnesia brlckcomposed essentially of a mixtureofparticles of chrochromite; (molding the mixture into bricks and jbaking the bricks. v 2. In the process oi making chromite-magma;-slabrick having unprecedented spallingresistance, great slag resistanceand strength' at high temperatures, and fair strength at atmospherictemperatures, the improvement which comprises adjusting the proportionof the sizes of particles in a material consisting essentially of groundchromite and ground magnesia in which the amount of said chromite isgreater than" i such a mannerthat the mixture will contain at mite "and,magnesia in which the weight/oi said chromitesubstantially exceedsthe-weight of the i L magnesia, an'd-in which 40' 1 the proportion 01'-fine material, initially smaller than 100;; (passing through a 150 meshper linear inch screen) is at least about 20 to 40 parts, the proportionof intermediate iiiaterial of initial particlesizes between 100 and 1000(between a 150 and 16.mesh

per linear inch screen) andthe proportlonjof is not over 15 to 25 partscoarse material of initial vparticlesize above 1000; (retained on a 16mesh leastabout 20 to 40 partsoi a fine fraction com- I:

posed of particles of a sizebelo'w, 100p (passing through a 150 mesh perlinear men" screen), not over 15 to 25 parts of anintermedlatefractioncomposed of particles of a size between about 100 and about 1000(between a 150 and 16 mesh per linear inch screen) and at least about35to parts of a coarse material composed of particles of a size aboveabout 1000p. (retained ona 16 mesh per linear inch screen), the whole ofthe magnesia being in a fine condition substantially below 100, (passinga 150 mesh per 'linearfinch screen), the marginal sizes between twoadjacentffractions being omitted, whereby there isa substantial jump ingrain size between the smallest particles in the next coarser fractionand the largest particles in the next finer fraction; molding themixture into bricks and baking the bricks.

3. A process as in claim 2, in which the jump V in grain size betweenthe smallest particles in the next coarser fraction and the largestparticles in j the next finer fraction amounts to 400 to 1000corresponding to the difference between a 35 and 16 mesh per linear inchscreen. 4. In the process of making chromite-magnesia brick havingunprecedented spalling resistance,

per linear. inch screen) parts, substantially all of the magnesia beingin a fine condition of initial whereas the said ,fine fractionbelowabout 100 contains substantially no chromite, said brick beingcharacterized by having a spelling resist:

ance of not below 30. l

8, Refractory chromite-magnesia brick, com- 40 parts of a fine fractionsubstantially consisting of magnesia particles of an initial particlesizebelow aboutlOOa (passing through a mesh per linear inch screen), andof about 60 to 80 parts of a coarse fractionsubstantially composed ofchromite par-. ticles of an initial particle size above, about 1000;(retained on a 16 mesh per linear inch screen).

9. In the manufacture of refractory molded products suitable for usewithout previous kiln firing, composed principally of chromite and bu d.over the magnesite, which processcomprises pre paring a mixtureconsisting essentially of 20 to 40 parts of fine material which willpass a 150 mesh manner that the mixture is at least about 35 to 65particle size below about magnesite, the chromite predominating moldi'ngsuch mixture under a pressure of at least 2843 lbs. per sq. in., dryingthe molded products.

10. A dry molded chrome-magnesia refractory having very high resistanceto spelling, such prod.- uct consisting essentially of to parts of finematerial which will pass a 150 mesh screen, and 80 to parts of coarsematerial which will be retained on a 16 mesh screen, 20 to 40% of theentire, mixture being burned magnesite which exists chiefly as finergrain fraction, and the re.- mainder being essentially chromite, whichproduct is suitable for use in the unfired condition.

11. In the process of making chromite-magnesia brickhavin-g'unprecedented spelling resistance, great slag resistance andstrength at high temperatures, and fair strength at atmospherictemperatures, the improvement which comprises adjusting the proportionoithe sizes of particles in a material consisting essentially of groundchromite and ground magnesia, in which the amount of said chromite isbetween 60 and in such a manner that the mixture will contain at leastabout 20 to 40 parts of a iine fraction composed of particles of a sizebelow a (passing through a mesh per linear inch screen), and at leastabout 35 to 65 parts of a coarse material composed of particles of asize above about 1000p (retained on a 16 mesh per linear inch screen),over one-half of the said magnesia being in a fine condition below about100a (passing through a 150 mesh per linear inch screen) and suchmaterial being entirely free from any intermediate'fraction composed ofparticles of a size between about 100; and about 1000, (between a 150and a 16 mesh per linear inch screen) molding the mixture into bricksand baking the bricks.

KONRAD ERDMANN.

